2 Answers

http://myfwc.com/wildlifehabitats/managed/american-crocodile/croc-or-gator/ 

Here's a bit of interesting trivia for you: All alligatorsare crocodiles, but not all crocodiles are alligators. Sound confusing? It's really not once you look at the taxonomy.

Both alligators and crocodiles are members of the reptilian order Crocodylia. But the families they belong to, Alligatoridae and Crocodylidae respectively, differ. Often, when people use the word "crocodile" what they really mean is "crocodilian." This term encompasses not just the common alligators and crocodiles you might already know, but also the lesser known Gavialidae family that contains the lone gavial, or gharial. All told, there are 23 species of crocodilians.

http://animals.howstuffworks.com/reptiles/alligator-vs-crocodile.htm

Crocodiles tend to have a longer, narrower, snout than alligators. And crocodiles tend to come from the nile river area and from India. Whereas, Alligators tend to come from the southern U.S., and the carribean, and the Congo.